help with framing

I recently bought a John Haney photograph there Artsy, and have had it framed.  It is a long piece, say, 2 feet by 15".  It is matted but not mounted.  It is rippling without being mounted.  How do the professionals mount their work so that it does not ripple.  Reversible mounting has been discussed but there seems to be some controversy over whether this is a good method for an investment piece.  Any guidance is appreciated.  Thanks, Christine.